1. Field of the Invention
This invention relates to breakaway coupling assemblies, and more particularly, to frangible valve fittings for such assemblies. Specifically, the present invention relates to an improved breakaway valve fitting which is self-closing and includes a frangible coupling.
2. Description of the Prior Art
In the transporting of fluids, either liquids or gases, certain applications require that the fluid conduits be capable of fracturing or separating at predetermined locations for safety purposes. Such requirements are common in the aircraft industry and in other applications wherein, in the event of an accident, collision or crash, it is desired that fuel lines and other conduits containing flammable liquids or gases separate from the tanks or reservoirs which carry such liquids or gases. This is in order to minimize the spillage of such flammable liquids and reduce fire hazards as well as improve the control of fires. Such breakaway valve fittings may be located within fuel lines themselves or at the junction of fuel lines and tanks or reservoirs, such junction points commonly being the weakest juncture in the entire fuel system, thereby representing the weakest link wherein the greatest chance of fracture would normally occur.
In the past, frangible valve fittings have been used to provide the weakest juncture point in a fuel line. In this manner, should fuel line separation occur as a result of an accident, such separation would occur at the frangible valve fitting. This valve fitting, therefore, would automatically seal the passageways of the fuel line upon fracture of the frangible members, thereby preventing the escape of fuel contained in the fuel line and the fuel tanks.
In the past, such frangible valve fittings have often utilized poppet-type valves placed within the fitting body passage. While such poppet valves are generaly capable of sealing the fitting passage, their design and construction produces relatively high resistance to flow through the passage, and may create undesirable turbulence during normal operation. In addition, known frangible valve fittings often utilize relatively close tolerances between components intended to move relative to each other during operation, and in view of the fact that long periods of time may exist between operation of the valve components of the fittings, the components may corrode or otherwise limit movement relative to each other rendering the device inoperative when needed.
U.S. Pat. No. 4,090,524 discloses a frangible valve fitting which incorporates a flapper valve with a poppet valve to insure closure movement. However, a distinct problem with flapper valves is that should pieces of the fractured frangible elements or any other debris become lodged in the valve openings prior to complete closure of the flapper portions, the valves will not close entirely. Furthermore, a large amount of movement is required to move the flapper valve member from its open position to its closed position, thereby allowing substantial amounts of fuel to leak prior to full closure of the valve.
U.S. Pat. No. 3,921,656 discloses a self-closing breakaway valve which utilizes a pair of ball valves which are rotatable upon release of a trigger device upon separation of the valve housings. While this design overcomes several of the problems associated with prior self-closing breakaway valve assemblies, this design also includes certain disadvantages. One such disadvantage is that the ball valves of this particular device do not move so as to positively close against a valve seat. Therefore, should the preload of the spring member which rotates the ball valve be reduced during the course of time, the ball valve may not be fully rotated against a high internal fuel pressure when the device eventually becomes needed. Thus, the valve would not fully close.